1. Field of the Invention
The present invention relates to device and method for controlling ignition timing of an internal combustion engine, and particularly to a technique of controlling ignition timing based on whether knocking is present or absent.
2. Description of the Background Art
Conventionally, various methods of determining whether knocking (knock) is present or absent have been proposed. For example, there is a technique of determining occurrence of knocking based on whether or not magnitude of vibration detected in an internal combustion engine is greater than a knocking determination value. A knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-021032 includes: a knock sensor detecting knocking in an internal combustion engine; a statistical processing portion statistically processing an output signal detected by the knock sensor; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the output signal detected by the knock sensor; and a final determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final determination portion finally determines that knocking has occurred. In the first temporal determination portion, by comparing the maximum value of the output signals detected by the knock sensor with a knock determination level calculated based on the processing result by the statistical processing portion, whether or not knocking has occurred is determined. A knock determination value is corrected to a value obtained by subtracting a set value ΔV from the knock determination value or to a value obtained by adding the product of a value A greater than “1” and set value ΔV to the knock determination level, based on the occurrence frequency of knocking.
According to the knock control device disclosed by the publication, a knock temporal determination by a statistical processing program and a knock temporal determination by a waveform shape program are used, and only when both of the temporal determinations determine that knocking has occurred, it is finally determined that knocking has occurred. As a result, occurrence of knocking can precisely be determined even as to an output signal, which has been erroneously determined by a knock determination employing solely the statistical processing program or the waveform shape program.
However, even when whether knocking is present or absent is determined using a knock determination level (determination value) that is corrected according to the occurrence frequency of knocking as in the knock control device described in Japanese Patent Laying-Open No. 2003-021032, not always the presence or absence of knocking is precisely determined. For example, in starting the internal combustion engine, if an initial value of the determination value is greatly different from magnitude of vibration occurring in the internal combustion engine, whether knocking is present or absent may not be determined precisely until the determination value is corrected. During the period in which whether knocking is present or absent cannot be determined precisely, ignition timing is unduly retarded or advanced. Accordingly, ignition timing cannot be controlled appropriately.